The invention relates generally to thermal shrouds for gun tubes and, in particular, to a thermal shroud for minimizing a temperature gradient across a gun tube due to both internal and external heat flux asymmetries.
In rapid fire small arms, such as machine guns, it is often necessary to use a cooling system or apparatus to remove heat from the gun barrel caused by rapid firing of the weapon. One method of removing this internally generated heat is to surround the gun barrel with a thermally conductive material, such as aluminum, in intimate thermal contact with the gun barrel, to distribute this heat both axially and radially, and to provide a large exterior surface for radiating this heat to air passing over this surface. Examples of such cooling apparatus are described in U.S. Pat. No. 2,112,144, issued Mar. 22, 1938 to Coupland, and in U.S. Pat. No. 2,337,840, issued Dec. 28, 1943 to Scott-Paine et al.
In larger guns, such as tank cannons, temperature gradients across the tube due to external heat flux asymmetries, such as uneven heating caused by solar or ground radiation, or uneven cooling caused by rain, sleet, or wind, can cause slight bending of the gun tube which contributes to aiming inaccuracy. All successful thermal shrouds for minimizing the temperature gradient across the gun tube due to external heat flux asymmetries utilize one of two design principles. One method is to azimuthally disburse the gradient by using a thermally conductive outer shroud layer. The other method is to thermally shield the barrel from external temperature gradients by providing adequate radial insulation between the gun tube and the outer shroud surface. For example, the heat pipe jacket described in U.S. Pat. No. 4,346,643, issued Aug. 31, 1982 to Taylor et al, employs conductive dissipation while the thermal sleeve described in U.S. Pat. No. 4,638,713, issued Jan. 27, 1988 to Milne et al, relies on radial insulation. Some designs, such as the BRL thermal jacket shown in FIG. 3 herein, employ both mechanisms by alternating thermal insulating and conducting layers.
Conventional shrouds which thermally insulate the barrel from external temperature gradients have some type of thermal insulation, such as thermal insulating material or a closed air space, adjacent to the gun barrel. While this layer of insulation protects the barrel from the influence of temperature gradients at the shroud outer surface, it does not help dissipate barrel temperature gradients generated internally from gunfire.
Also, in conventional shrouds which azimuthally disperse a temperature gradient across a gun tube by the use of a thermally conductive layer extending about and along the tube, this thermally conductive layer is usually formed as a cylindrical element of solid metal. Thus, any temperature difference across this solid metal layer due to an asymmetric heat flux will exert some bending force on the gun tube.